1. Field of the Invention
The present invention relates to a method and a device for enhancing the signal-to-noise ratio of ECG signals.
2. Description of the Prior Art
ECG signals recorded on the exterior of the body always contain extensive noise originating from muscular activity, digitization of the recorded analog ECG signal, the recording instruments and influence from the power supply. Using modern technology, however, the two latter sources of noise can be largely eliminated. Noise from the muscular activity of the patient and the digitization procedure, however, often drowns out low-amplitude signal components in the ECG signal.
In an effort to reduce noise, and thus to improve the signal-to-noise ratio for these low-amplitude signal components, it is known to subject the ECG signals to different kinds of averaging procedures. Time-varying Wiener filtration has also been attempted in order to enhance the signal-to-noise ratio, see Weerd and Martens: "Theory and Practice of A Posteriori Wiener Filtering of Average Evoked Potentials", Biol. Cybern., 30, pp. 81-94, (1978), and Weerd and Kap.: "A Posteriori TimeVarying Filtering of Averaged Evoked Potentials", Biol. Cybern., 41, pp. 223-234, (1981). This technique is based on the estimated signal and noise effects determined for different frequencies. In this process, some spectral loss is unavoidable in the Fourier transform procedure utilized. With low signal-to-noise ratios, this method also results in a consistently erroneous identification of the sought signal contained in the noise.